In a typical electronic module for use in an automobile, electronic components carried on a printed circuit board are sealed by encapsulation within a layer of potting compound. Commonly in such a module, certain components such as power transistors are attached to heat sinks which extend through the potting compound layer. In use of such modules, the potting compound may lose adhesion to the heat sink due to stress caused by incompatible thermal expansions during deep thermal cycles. The separation caused by this loss of adhesion can act as a leakage path for the ingress of external water to the module, causing malfunction.